The present invention relates to an improved sewage separation system. Specifically, the invention involves an improved preloader tank for separating waste materials collected from restaurants, hotels, condominium complexes or the like that produce mixed sewage, including waste water, oleaginous materials and solids, in a common line.
Some buildings drain all of their sewage into common lines that feed to public sewers. This causes oleaginous materials (grease and oil), common in kitchen waste, to be mixed with human waste. Most sewage treatment plants are not intended to handle oleaginous materials. In addition, the oleaginous materials may cause build-ups in the lines leading to the treatment plants, which could result in blockages. Accordingly, it is preferable, and many local codes require, that any sewage draining into public sewer lines not contain any significant concentration of oleaginous materials.
Oleaginous waste usually may be disposed of at public dumps. However, for public health and safety reasons, it is not permissible to dispose of human waste at public dump sites. Therefore, oleaginous materials often must be removed from the rest of the sewage before it is discharged into public sewer lines and processed at sewage treatment plants.
It is also useful to grind solid waste material before discharging it into public sewer lines. In this way the solids will be less likely to lodge in the lines and cause blockages downstream.
There are preloader tanks known in the art for separating the contents of raw sewage, to some degree, into oleaginous materials, waste water, and solids, examples of which are shown in U.S. Pat. Nos. 5,360,555, 5,543,064, 4,940,539, 5,254,267 and 5,505,860.
U.S Pat. No. 5,360,555 (Batten '555) shows a typical design of a tank for separating waste materials as discussed above, although the tank in Batten '555 is of limited size and specifically intended to handle sewage from kitchens only. Batten '555 discloses a separator tank that uses first and second chambers to separate waste water, oleaginous materials and solids. The first chamber has a sloped bottom leading to an outlet attached to a grinder, such as a garbage disposal, for the removal of solids. The first chamber is separated from the second chamber by a weir and a first baffle. Water and oleaginous materials flow over the weir and under the first baffle to reach the second chamber. A screen prevents the movement of solids into the second chamber. The second chamber includes an oleophilic disk for removing oleaginous materials from the surface of the water and a second baffle under which water flows to reach a discharge line. The ground solids from the grinder are pumped to the discharge line and remixed with the waste water.
U.S. Pat. No. 5,543,064 (Batten '064) shows a similar, but much larger, tank than the one shown in Batten '555. Specifically, the Batten '064 patent discloses a sewage lift station. Lift stations are tanks attached to public sewer lines that pump sewage to a higher elevation so that the sewage may flow by the force of gravity through the sewage line to the treatment plant. Batten '064 discloses a lift station that includes a solids separation chamber, a separation chamber for oleaginous materials, and a sewage lift chamber. The solids separation chamber, which is separated from the separation chamber for oleaginous materials by a wall, includes an inlet, screen and pump. Once waste materials enter the solids separation chamber through the inlet, solids are prevented by the screen from spilling over the wall and are pumped into the sewage lift chamber by the pump. Oleaginous materials and water flow over the wall into the separation chamber for oleaginous materials, where a skimmer removes the oleaginous materials and a water conduit allows the water to flow into the sewage lift chamber. A pump pumps the water and solids from the sewage lift chamber to the higher elevation.
These known separation systems have a number of drawbacks that can cause problems downstream at the sewage treatment plants. Particularly in growing communities, the sewage treatment plants must deal with increasing amounts of sewage. If the load at the treatment plant becomes too great, bacterial colonies used to process the sewage become overworked, and hence cannot handle the volume of sewage. This causes a greater retention time of the sewage at the treatment plant. Additionally, the bacterial colonies are disturbed by turbulence when sewage enters the treatment plant with too much force or velocity. The treatment plants are designed to handle sewage that moves through the lines with only the flow pressure caused by gravity.
These downstream problems are often caused or exacerbated by the use of separation (preloader) tanks like those discussed above. Generally, the pumps in these tanks activate when the tanks fill with sewage, which occurs most often at peak usage times during the day, usually in the mornings and afternoons. Accordingly, many of these systems can activate at the same times each day. This can cause surges in the volume of sewage reaching sewage treatment plants during the peak times. The bacterial colonies at the treatment plant work more efficiently if they receive a relatively steady source (flow rate) of nutrients, rather than surges. Also, the flow pressure generated by the pumps can propagate through the sewer lines to the treatment plants, causing unwanted turbulence. The present invention alleviates these and other problems associated with known preloader systems.
The sewage separation system of the present invention is an improvement upon those systems that comprise the following elements or features: a chamber for receiving sewage containing water, oleaginous materials and solids, in which at least a portion of the solids can settle to the bottom of the chamber and a portion of the oleaginous materials can rise to the top of the water; a discharge line for passing the sewage from the sewage separation system into a transport line that leads to a sewage treatment plant; means for grinding at least a portion of the solids that settle to the bottom of the chamber; a conduit for conducting a slurry of the ground solids in water from the chamber to the discharge line; and means for preventing at least a portion of the oleaginous materials that enter the system from entering the discharge line.
In the present invention such a system is provided with a pressure relief line running from the conduit through which the slurry of ground solids is conducted from the chamber to the discharge line. The pressure relief line is in communication with the sewage-receiving chamber, so as to allow head pressure in the conduit to be released into that chamber. By virtue of the inclusion of the pressure relief line, excess flow pressure can be released back into the system before the sewage reaches the transport line.